An in-plane switching (In-Plane Switching: IPS) (registered trademark) mode is a method in which a lateral electric field is applied to a liquid crystal layer held between substrates opposite to each other so as to perform display. Because the IPS mode is excellent in viewing angle characteristics as compared with a TN (Twisted Nematic) mode, the IPS mode is considered as a display method which can further improve an image quality. On the other hand, because a pixel aperture rate of the liquid crystal display device of the IPS mode is difficult to be made large as compared with the liquid crystal display device of the normal TN mode, the liquid crystal display device of the IPS mode has a disadvantage that a light utilization efficiency is low. This is due to the common configuration of the liquid crystal display device of the IPS mode, in which a pixel electrode and a counter electrode made of a nontransparent metal film are disposed on the same layer on the same substrate.
As a liquid crystal display device which can improve the above-described problem with respect to the light utilization efficiency, a fringe field switching (FFS) mode is proposed. In a liquid crystal display device of an FFS mode, the pixel electrode and the counter electrode are disposed in the same substrate similarly to the liquid crystal display device of the IPS mode; however, the pixel electrode and the counter electrode are made of a transparent conductive film, whereby the light utilization efficiency is improved. Further, because of a large capacitance between the transparent conductive films, a holding capacitance forming region does not have to be provided. In this case, because a transmittance of light can be improved, the light utilization efficiency is further improved.
In general, the pixel electrode and the counter electrode used in the TN mode have a simple layer structure. Compared to this, the pixel electrode and the counter electrode used for the IPS mode are a pair of comb-tooth electrodes which are disposed on the same layer with a gap therebetween so as to engage with each other. Further, the liquid crystal display device of the FFS mode has a lower electrode and an upper electrode in which many slits are provided to face the lower electrode. The comb-tooth structure or the slit structure can create concavity and convexity on a surface of an array substrate of the liquid crystal display device. Due to this concavity and convexity, a rubbing treatment of an alignment film provided on the surface of the array substrate is likely to be uneven. As a result, the alignment of the liquid crystal molecules is in disorder; thus, there is caused a display defect in the liquid crystal display device such as decrease in contrast or light leakage.
Therefore, there is proposed a technology for reducing the concavity and convexity on the surface. For example, according to Patent Document 1 (Japanese Patent Application Laid-Open No. 2003-131248), an insulating film is formed to fill in between the electrode fingers by using chemical mechanical polishing. Further, for example, according to Patent Document 2 (Japanese Patent Application Laid-Open No. 2010-2594), a pixel electrode in a comb-teeth shape is formed in the recessed part of an inter-layer insulating film by using a lift-off method.